Nato's top military commander says Russia is ready to invade Ukraine and could "accomplish its objectives" in three to five days.

Nato's Supreme Allied Commander Europe, US Air Force General Philip Breedlove, said the organisation had spotted signs of movement by a very small part of the Russian force overnight but no indication that it was returning to barracks.

Gen Breedlove said the situation is "incredibly concerning" as Russia has all the forces it needs on Ukraine's border if it decides to carry out an "incursion" into the country.

Nato foreign ministers meeting in Brussels have asked the general to draw up a package including land, air and sea reinforcements to reassure nervous allies in eastern Europe by April 15.

His comments came as Nato suspended all practical cooperation with Moscow in protest at its annexation of Crimea from Ukraine.

Russia has responded by accusing the alliance of reverting to the language of the Cold War and said neither side would gain from the move.

Image Caption:A Russian soldier directs a tank after its arrival in Crimea

"The language of the statements rather resembles the verbal jousting of the Cold War era," Foreign Ministry spokesman Alexander Lukashevich said in a statement.

He said the move sparked a sense of deja vu - referring to Russia's five-day war with Georgia in 2008, when Nato withdrew cooperation but later resumed it of its own accord.

Video:What Crimea's History Tells Us

Mr Lukashevich said: "It is hard to imagine who will gain from the suspension of cooperation between Russia and Nato on countering modern threats and challenges to international and European security, in particular in areas such as the fight against terrorism, piracy and natural and man-made disasters.

"In any case, it will certainly not be Russia or Nato member states."

The diplomatic row comes a day after Russia signalled it would pull back some troops massing on the Ukraine border.

Video:How Did Ukraine Get Here?

The German government said President Vladimir Putin had assured Chancellor Angela Merkel that he had "ordered a partial withdrawal" of military forces.

Western fears of a new incursion into eastern or southern Ukraine by Moscow have been growing since last week, when a build-up of Russian troops along the border was seen.

The Wall Street Journal reported that Russian troops gathering on the border were concealing their positions and establishing supply lines that could be used in a prolonged deployment, according to officials briefed on the latest US intelligence.

Video:Russians Fire Shots At Crimea Base

The assessments prompted concerns that Russia is preparing to invade Ukraine without warning, rather than carrying out military exercises as it has claimed.